Nine people were killed when floodwaters from a sudden rainstorm thundered through a tranquil swimming area in Tonto National Forest.

Crews continue to search Sunday afternoon for a person still unaccounted for, a day after the flash flood hit the Cold Springs canyon, located about 100 miles northeast of Phoenix.

The popular cooling spot, known as the Ellison Creek or Water Wheel swimming holes, is accessible through several hiking trails. It is about 20 feet wide and 20 feet long with a waterfall above it.

It isn’t the first time people have been killed when flash floods swept through so-called slot canyons, which are formed by the wear of water in rock and are typically significantly deeper than they are wide.

Here’s a look at other deadly flooding incidents in slot canyons in the U.S. during the past few years:

Flash flood at zion national park

Seven people were killed in Utah’s Zion National Park in September 2015 when they were tapped during a sudden flash flood while hiking. The group was trapped by floodwaters in a popular slot canyon that was as narrow as a window in some spots and went several hundred feet deep.

A park ranger said at the time that the flooding went from a “trickle to a wall” of water. The group — comprised of hikers in their 40s and 50s — had set out on their trek hours before a flash-flood warning prompted park officials to close the canyons.

A Ventura, County, California, sheriff’s sergeant, Steve Arthur, was among those killed.

Couple swept away in flash flood

A husband and wife from California were killed in September 2008 when they were trapped in a flash flood while hiking in a slot canyon in the Grand Staircase Escalante National Monument in Utah.

Authorities said Gordon and Kathy Chapple of Walnut Creek, California, had been hiking in the canyon with their children when the flood hit. The couple, in their 60s, was swept away in the flood. Their bodies were later found in downstream drainage.

The rest of the group clung to canyon walls and was able to climb out.

Rainstorm At Lower Antelope Canyon

Eleven hikers were killed in August 1997 when a 40-foot-high wall of water from an unexpected rainstorm boomed through a narrow, twisting series of series of corkscrew-curved walls known as Lower Antelope Canyon, near Page, Arizona.

Some of the hikers were washed four miles down the canyon, which is on Navajo land.

The hikers included two people from the U.S., seven from France, one from Britain and one from Switzerland, officials said at the time.